Selective call receivers, including pagers, are typically used to alert a user of a message by producing an audio alerting signal. However, the audio signal may be disruptive in various environments and therefore, vibrators have been utilized to provide a silent alerting signal.
Vibrator motors are well known in the art and generally comprise a cylindrical housing having a rotating shaft along a longitudinal axis attached to an external unbalanced counterweight. Vibrator motors have proven successful for alerting a user of a received message, but conventional designs have been unreliable due to failure of the mechanism initiating the vibration, typically the unbalanced counterweight.
FIG. 1 of the drawings is a typical example of a conventional vibrator motor. Referring to FIG. 1, a conventional vibrator motor 100 comprises a cylindrical body 102, a longitudinal, rotating shaft 104, and an unbalanced, rotating counterweight 106. The cylindrical body 102 is held in place on a printed circuit board 108 by motor bracket 110. The counterweight 106 is attached to the protruding end of the shaft 104 on the vibrator motor 100. Operationally, the motor 100 is energized by a power source causing the shaft 104 and the counterweight 106 to rotate, resulting in the motor 100 vibrating and, consequently, the selective call receiver vibrating.
With the trend to miniaturization, the vibrator motor has become the largest component in silent alert pagers. It is, therefore, not possible to further significantly reduce the size of a silent alert pager unless the vibrator motor is reduced in size. However, it is important that the vibration level not be reduced since this would defeat the advantage of the size reduction.
To overcome the problems with the conventional vibrator motor, an electromagnetic resonant vibrator has been utilized as the frequency controlling element for generation of an alerting signal and also as a frequency responsive device that responds to a given signal. Such devices have included a vibratory member, such as a reed, having a natural resonant frequency, with a magnetic structure coupled thereto which causes vibrations of the reed at its natural resonant frequency. Electromagnetic resonant vibrators have also been proposed wherein an armature is mounted for lateral or rotary movement. The magnetic structure for such devices may include a first coil for exciting the armature, and a second coil for picking up signals in response to the vibrations, so that signals are coupled therebetween only at the resonant frequency of the vibratory member. The device must also provide isolation of the critical components from external shock and vibration influences. For example, if the unit is dropped or jarred, the reed should not vibrate and provide a response as though a signal had been received. These previously known devices were unstable; therefore, the systems were not resonant and their restoring force unbalanced, resulting in a larger power consumption than necessary.
Thus, what is needed is an improved vibrator in a selective call receiver for alerting a user of a received message.